My vet keeps them overnight for both males and females. They say it is to monitor them in case of complications from the anesthetic and so that they can sedate them if they become overly aggitated where they might hurt themselves. I have never had any ill effects from them staying overnight, but my kitties are pretty laid back. My vet has someone there overnight. If nobody is going to be in the clinic anyway I would definately insist on taking him home that night.
